Solar Cycle Related Changes in the Helium Ionization Zones of the Sun

TL;DR

This study analyzes helioseismic data across two solar cycles to detect and characterize changes in the Sun's helium ionization zones associated with solar activity, using improved data fitting techniques.

Contribution

It provides the first clear evidence of solar cycle-related changes in the helium ionization zones based on two solar cycles of helioseismic data.

Findings

Detected changes in the HeII ionization zone correlated with solar activity.

Confirmed the variability of solar interior structure over solar cycles.

Improved analysis techniques enhanced the detection of subtle structural changes.

Abstract

Helioseismic data for solar cycles 23 and 24 have shown unequivocally that solar dynamics changes with solar activity. Changes in solar structure have been more difficult to detect. Basu & Mandel (2004) had claimed that the then available data revealed changes in the HeII ionization zone of the Sun. The amount of change, however, indicated the need for larger than expected changes in the magnetic fields. Now that helioseismic data spanning two solar cycles are available, we have redone the analysis using improved fitting techniques. We find that there is indeed a change in the region around the HeII ionization zone that is correlated with activity. Since the data sets now cover two solar cycles, the time variation is easily discernible.